What does showgrid=top leads to? It will include \psgrid at the end of the pspicture-environment. This may be the problem, as everything gets shifted by drawing the grid at the very end...
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DL6ERApr 4 '13 at 12:27

Yes. But in general, showgrid activated in pspicture is for navigational purposes when constructing the diagram. For me, showgrid=bottom or showgrid=top should take unit defined outside the pspicture. And \psgrid should be used for other purposes. It is just an opinion. :-)
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kiss my armpitApr 4 '13 at 13:51